Conventionally, as raw fat materials for plastic fat compositions such as margarines, shortenings and the like (hereinafter, abbreviated as M/S), partially hydrogenated oils of vegetable/animal fats, i.e., so called hydrogenated oils, have been commonly used. However, in recent years it has been elucidated that trans fatty acids which are produced in a hydrogenation reaction and are included in hydrogenated oils may increase the risk of cardiac diseases and the like, and thus demands for M/S from which trans fatty acids are eliminated to as less as possible have rapidly increased.
In order to reduce the trans fatty acid level in M/S, candidates for fats that can be an alternative of hydrogenated oils are significantly limited, and have been restricted to palm oils in effect. Although palm oils are effective in maintaining the hardness of M/S since they are present in the form of a semisolid or a solid at ordinary temperatures, on the other hand, when they are used as a raw fat material of M/S, they are problematic in that roughening of the texture and formation of crystals of coarse particles (coarse crystals) may be caused during storage of the product, thereby resulting in deterioration of appearance and physical properties of the product, and roughness of the texture.
With respect to the aforementioned coarse crystals generated in M/S produced using a palm oil, POP (1,3-dipalmitoyl-2-oleoylglycerol) that is a major triglyceride of the palm oil corresponds to the major constitutive component of the coarse crystals; therefore, reforming processes by transesterification aiming at reduction of the POP content have been conventionally investigated in attempts to reform a palm oil except for hydrogenation (for example, see Patent Documents 1 to 3). In addition, processes for precluding coarse crystals by adding a certain emulsifying agent have been also investigated (for example, see Patent Documents 4 and 5).
In the case of reforming by transesterification of a palm oil as disclosed in Patent Documents 1 to 3, the POP content can be significantly reduced to improve the crystallinity according to a reaction in which sodium methoxide is used as a catalyst. However, a problem of inferior melt-in-the-mouth may be caused as indicated by a curve drawn by plotting the solid fat content (hereinafter, referred to as “SFC”) with respect to the temperature approximating a horizontal curve. In addition, according to transesterification by lipase specific for 1,3-position, the POP content cannot be significantly reduced, and thus the effect of reforming crystallinity cannot be achieved satisfactorily.
In the processes for precluding coarse crystals of a palm oil by adding an emulsifying agent disclosed in Patent Documents 4 and 5, a comparatively large amount of emulsifying agent must be added in order to achieve the effect of precluding the coarse crystals. Therefore, an unpleasant flavor of the emulsifying agent that affects the M/S product can be disadvantageous.
Therefore, development of techniques for reforming the crystallinity of palm oils which can directly take advantages of features of the palm oils (favorable melt-in-the-mouth, and plain flavor) has been desired.
Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S55-110195
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. H02-219581
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. H10-183165
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. S62-205738
Patent Document 5: Japanese Unexamined Patent Application, First Publication No. 2007-124948